The present invention relates to a zoom lens system, and more particularly a so-called rear stop diaphragm type zoom lens in which a stop diaphragm is disposed behind the lens system on the image side and a position of the stop diaphragm is maintained constant with respect to the image focusing surface during the variation of magnification.
Recently, zoom lenses have remarkably been developed particularly for single lens reflex cameras and there have been various type lenses having various view angle ranges. However, any of these lenses has a stop diaphragm disposed in its lens system. The above described rear stop diaphragm type zoom lens is not known. This is due to the fact that the rear stop diaphragm type zoom lens is perfectly asymmetrical with respect to the position of the stop diaphragm and a part of the optical system must be moved during variation of magnification. As a result, the asymmetry is also varied to cause the aberration compensation to be difficult. In addition, since generally the overall physical size of the zoom lens tends to be increased, the inlet pupil of the rear stop diaphragm type is deep to result in an increase of the diameter of the front lens. This leads to difficulty of miniaturization disadvantageously. On the other hand, since the stop diaphragm is not interposed in the lens system, the mechanical construction is extremely simplified so that the lens can be produced with low cost. Due to this economical advantage, it is very effective to use such a lens system as an interchangeable zoom lens, particularly for the SLR camera in which a stop diaphragm is disposed in a body.